:''For the book by
William S. Burroughs, see
Tornado Alley (book).

An outline of Significant Tornado Alley in the United States, where the highest percentage of violent tornadoes occur
'Tornado Alley' is a colloquial term most often used in reference to the area of the
United States in which
tornadoes are most frequent. Although an official location of the term is not defined, the areas in between the
Rocky Mountains and
Appalachian Mountains are the areas usually associated with it.
Tornado geography
Although no
state is entirely free of tornadoes, they are most frequent in the
Plains area between the Rocky and Appalachian Mountains and in the state of
Florida. The state where twisters most commonly occur is
Texas (notably due to its size of where tornadoes can occur).
[ TORNADO NUMBERS 1950 - 1994 ] When land area is taken into account, however,
Florida has the highest density of tornado occurrence in the country.
[ Tornado Climatology ] However nearly all of Florida's tornadoes are weak, short lived and not produced by
supercell thunderstorms;
Oklahoma has the highest occurrence of such "classic" supercelluar tornadoes. In contrast, the
Northeast and
West tend to be the least tornado-prone regions in the United States.
Definition

Tornado activity in the United States.
Although Tornado Alley is generally considered to be in the areas of the
Central United States, no official definition of the term has actually been produced by the
National Weather Service. There are several ''ideas'' of what tornado alley is, but those ideas are the result of the different criteria used to come up with them.
Significant Tornado Alley
Perhaps the most common definition of tornado alley is the location of where the strongest tornadoes occur most frequently. In the United States that location is from
Texas, northward through
Oklahoma,
Kansas,
Missouri,
Nebraska and into
South Dakota. However, states to the east have experienced many F5 tornadoes since 1950 such as
Iowa, southern
Ohio, and northern
Alabama (
Birmingham, Alabama has actually been stuck by two F5 tornadoes).
[1]
Impact
In the heart of tornado alley,
building codes are often stricter than those for other parts of the U.S., requiring strengthened roofs and more secure connections between the building and its
foundation. Other common precautionary measures include the construction of
storm cellars, and the installation of
tornado sirens. Tornado awareness and
media weather coverage are also high.
References
1. F5 and EF5 Tornadoes of the United States
Other areas experience many strong tornadoes, but whereas strong tornadoes in the aforementioned area accrue more steadily, strong tornadoes in the Mississippi and Ohio Valleys and the Southeast occur less frequently but tend to surge in large outbreaks.
Other criteria
Another criteria for determining tornado alley is to not focus on just the strongest tornadoes, but the location of where tornadoes happen more frequently relative to other places in the county. When using this method tornado alley has a much wider reaching grasp. In addition to Significant Tornado Alley, this area can include the great lowland areas of the Mississippi, Ohio and lower Missouri River Valleys, as well as the Southeast into Florida.
Time of year
Also to be considered is the time of year. The highest frequency of tornadoes, commonly (but incorrectly) called "tornado season", shifts geographically depending on the season. During the winter months the Southeastern United States receives the highest number of tornadoes. During the months of March - May the threat shifts into the central United States. Then during the summer months the highest concentration of tornadoes tends to shift farther north as the weather warms across the U.S. Technically speaking, however, the central plains may be considered part of the tornado alley almost all-year-round, since this is where "temperature swings" between warm and cold air are most common.
Variations
The nickname Dixie Alley is sometimes used for the areas in the southern US - notably the lower Mississippi Valley and the upper Tennessee Valley - which are particularly vulnerable to strong/violent tornadoes. More people have been killed by tornadoes in this particular region than those of the great plains because of the higher population density in the southeastern U.S. "Dixie Alley" is used extensively by The Weather Channel.
Tornado Alley vs. Dixie Alley
See also
★
List of tornadoes and tornado outbreaks